About a year ago, dolphins Shadow and Chelmers died agonizing deaths in Connyland, Switzerland, after the zoo allowed a rave (attended by thousands) to be held near their training pool. For animals with sonar hearing, a possibly dubstep-heavy event was already considered a strain.

Now a toxicology report has emerged that shows a heroin substitute was found in the animal’s urine. This would seem to confirm initial suspicions that whacked-out ravers fed the dolphins drugs while possibly on some kind of weird acid trip.

AOL UK reports that it was originally believed that the techno music pumping out from the club just yards from the dolphins’ pool had caused their deaths:

But toxicology tests carried out by the forensics institute in St Gallen show that the heroin substitute Buprenorphin was present in the dolphins’ urine.

According to The Sun, Dutch marine biologist and dolphin expert Cornelis van Elk said: “Opiates are extremely dangerous for underwater mammals and would never be used in any legitimate treatment.